Pressure test question

[vavJETTAw36]

Decided to do a proactive boost pressure test today since I keep getting a code randomly for my rear oxygen sensors,that are coded out mind you (p1177 and p1178 lambda correction behind catalyst - threshold reached b1 and b2). What I find is I have to pump a lot of air in for it to build. I can build to about 15 psi before it stops building. Air dissipates to 0 in 15 seconds or so. Car doesn't have problems boosting and holding 25psi, so maybe it's the volume of air I'm pumping.

I can hear a leak coming from the disconnected pancake valve. Is this normal? I found a couple small ones in my Charge lines but not very big. Fixed those and now the only hissing I can hear is coming from inside one of those green check valves. It's the passenger side front most one that comes off the fuel rail. Not familiar with how the vac system works and the direction of boost but is it supposed to do this? Is this why I am hearing it from the pancake?


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[B501S4]

Pancake port needs to be capped off at the Y-pipe. You will hear it hissing as soon as you start to pressurize and see it drop pressure rapidly when you let off if it is not capped.


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[vavJETTAw36]

Pancake port needs to be capped off at the Y-pipe. You will hear it hissing as soon as you start to pressurize and see it drop pressure rapidly when you let off if it is not capped.


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Sorry, Didnt make that clear in the post.

Pancake port is blocked off. I can hear the air leaking from the disconnected Pancake. The loudest leak sounds like the green check valve is internally leaking. But maybe this is normal.

[Trb1]

Sorry, Didnt make that clear in the post.

Pancake port is blocked off. I can hear the air leaking from the disconnected Pancake. The loudest leak sounds like the green check valve is internally leaking. But maybe this is normal.

You shouldn't hear air getting by those green check valves. They're one way and should prevent pressure from escaping. Pull the end off the portion going to your intake manifold and blow into it and see if you can blow air by. If you can it's bad. If a lot of air is coming out of your pancake valve the pcv valve is probably bad as well.

[vavJETTAw36]

You shouldn't hear air getting by those green check valves. They're one way and should prevent pressure from escaping. Pull the end off the portion going to your intake manifold and blow into it and see if you can blow air by. If you can it's bad. If a lot of air is coming out of your pancake valve the pcv valve is probably bad as well.

Referring to the line off the distributor piece?

[Trb1]

Not the distributor piece, no. its labeled the "non return valve". if you have an early model b5 it will be the valve directly off the F hose. If its late model, it will be the valve off the line connected to the back of the intake manifold.

This guy here:

that check valve you here the hissing sound from will cause issues. I had boost flutter in partial throttle for 6 months until I deleted my whole N80 system and found out that particular green check valve completely gave way. The line that you pull off and blow into is the line between that green check valve you're hearing noise from and intake manifold. On the front of the car. Sorry for confusion.

[vavJETTAw36]

Not the distributor piece, no. its labeled the "non return valve". if you have an early model b5 it will be the valve directly off the F hose. If its late model, it will be the valve off the line connected to the back of the intake manifold.

This guy here:

that check valve you here the hissing sound from will cause issues. I had boost flutter in partial throttle for 6 months until I deleted my whole N80 system and found out that particular green check valve completely gave way. The line that you pull off and blow into is the line between that green check valve you're hearing noise from and intake manifold. On the front of the car. Sorry for confusion.

Ah gotcha yes its an early with the F hose. When you say blow into it you literally mean to blow with your mouth? This is enough pressure to check direction? Thanks for your help

[Trb1]

Not a problem. Yep! Just blow into the line. If you get any air by the check valve at all it is bad. you'll know if its good to go because it will be impossible to blow into.

[vavJETTAw36]

Not a problem. Yep! Just blow into the line. If you get any air by the check valve at all it is bad. you'll know if its good to go because it will be impossible to blow into.

That was it! Took it off and I could blow through the wrong way!

For anyone replacing this, do not buy the black check valves as they do not fit. I thought these were cheap replacements but nope. You'll have to spend the $30 on the plastic green one.


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[vavJETTAw36]

By the way it took about 30 seconds to go from 15psi to 0. Didn't sound like any other leaks but did hear sound coming from pancake. But this is probably just the crankcase venting pressure that passed around the Pistons and rings, right?


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